Datasheet

LM6588
www.ti.com SNOSA77D –MAY 2003–REVISED MARCH 2013
Application Notes
CIRCUIT DESCRIPTION
GENERAL & SPEC
The LM6588 is a bipolar process operational amplifier. It has an exceptional output current capability of 200mA.
The part has both rail to rail inputs and outputs. It has a −3dB bandwidth of 24MHz. The part has input voltage
noise of 23nV/√Hz, and 2
nd
and 3
rd
harmonic distortion of −53dB and −40dB respectively.
INPUT SECTION
The LM6588 has rail to rail inputs and thus has an input range over which the device may be biased of V
−
minus
0.5V, and V
+
plus 0.5V. The ultimate limit on input voltage excursion is the ESD protection diodes on the input
pins. The most important consideration in Rail-to-Rail input op amps is to understand the input structure. Most
Rail-to-Rail input amps use two differential input pairs to achieve this function. This is how the LM6588 works. A
conventional PNP differential transistor pair provides the input gain from 0.5V below the negative rail to about
one volt below the positive rail. At this point internal circuitry activates a differential NPN transistor pair that
allows the part to function from 1 volt below the positive rail to 0.5V above the positive rail. The effect on the
inputs pins is as if there were two different op amps connected to the inputs. This has several unique
implications.
• The input offset voltage will change, sometimes from positive to negative as the inputs transition between the
two stages at about a volt below the positive rail. this effect is seen in the V
OS
vs. V
CM
chart in the Typical
Performance Characteristics section of this datasheet.
• The input bias currents can be either positive or negative. Do not expect a consistent flow in or out of the
pins.
• The part will have different specifications depending on whether the NPN or PNP stage is operating.
• There is a little more input capacitance then a single stage input although the ESD diodes often swamp out
the added base capacitance.
• Since the input offset voltages can change from positive to negative the output may not be monotonic when
the inputs are transitioning between the two stages and the part is in a high gain configuration.
It should be remembered that swinging the inputs across the input stage transition may cause output distortion
and accuracy anomalies. It is also worth noting that anytime any amps inputs are swung near the rails THD and
other specs are sure to suffer.
OUTPUT SECTION
Current Rating
The LM6588 has an output current rating, sinking or sourcing, of 200mA. The LM6588 is ideally suited to loads
that require a high value of peak current but only a reduced value of average current. This condition is typical of
driving the gate of a MOSFET. While the output drive rating is 200mA peak, and the output structure supports
rail-to-rail operation, the attainable output current is reduced when the gain and drive conditions are such that the
output voltage approaches either rail.
Output Power
Because of the increased output drive capability, internal heat dissipation must be held to a level that does not
increase the junction temperature above its maximum rated value of 150° C.
Power Requirements
The LM6588 operates from a voltage supply, of V
+
and ground, or from a V
−
and V
+
split supply. Single-ended
voltage range is +5V to +16V and split supply range is ±2.5V to ±8.0V.
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